AFR range
 

I wanted to check what was the normal range for the mixture. Car is 1987 930 Turbo (original CIS system), with these items as it relates to the air/fuel:
1. Adjustable Leask WUR
2. Rebuilt fuel distributor from ************
3. Andial intercooler
4. TurboKraft K27 RS turbo
5. New O2 sensor
6. Checked for vacuum leaks
7. 1 bar boost
8. New spark plugs and cap
9. Cat delete

The car was surging/hesitating on hard acceleration before replacing the WUR and fuel distributor. I installed a digital Innovate MTX-L AFR gauge to better dial in the mixture.

My question is this, are these readings normal/acceptable:
-A little rough starting, but always starts
-Pulling away from the house, around 10.5 on the digital gauge
-Warming up through the neighborhood, cruising 2500 rpms in 2nd gear, 11.5-12.5
-After getting up to operating temps, I ran it hard on boost. In second gear as I get on acceleration hard, gauge goes up to 14.5 or so then as my rpms increase it comes down 13.5 then around 12.5 and then I shift
-Just cruising around in 3rd around 3000 rpms, gauge reads around 12.5
-Coming to a stop light, idling is around 9.8-10.2
-At idle, rpms hunt between 850 -1000 rpms

The car pulls hard and strong through boost. Just based on feeling, everything seems great but I want to double check. Exhaust smells a extra strong though in the garage (as in, if I'm in there after I shut the car down, almost brings tears to my eyes) and there's more soot on the tailpipes. Just put in 1/2 quart oil in about 500 miles. The shop ended up disconnecting the O2 sensor saying they "had difficulties achieving a proper mixture under light load and cruising with it connected- and then not also ending up with a super rich lopey smelly idle. The sensor was basically overriding our ideal targeted mixture and making us fudge in the wrong direction to correct." Also, takes a couple cranks for cold start but always starts and smooths out after 10 seconds of idle. The shop did say that I'm more on the rich side since they'd rather err in that direction.

Thoughts? Need adjustment or am I fine? Car seems to run great except for the strong exhaust smell and rough cold start.

Too rich at idle. Try something in the 13 range and see if the smell goes away.

I agree with this. More typical/normal would be idle mixture to be leaner than at full load, etc. Your at-load / high RPM / full boost readings look pretty good from here...

Other than improving smell and maybe the cold start (?), what benefits are there in adjusting the idle mixture? Or said another way, what would be the downside (other than smell) of not adjusting the idle mixture? I'm wondering if those readings are within acceptable range and therefore something that I can live with, considering everything else seems to be so dialed in. Or if there would be long term downsides to not adjusting that.

Down side? Bore wash..

It is way too rich in the lower rpms, and leaner than I would be comfortable with on boost


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Roger that. Considering the mods to my car, what would be the ideal mixture at idle and what mixture at higher rpms/boost? Does the fact that there's only a puff of smoke at startup, and nothing more, tell anything?

You need to move this to the turbo forum.

I chased AFR's for a while. You are too rich everywhere but on boost. There are some good threads in the turbo area.

This is probably one of the better threads
https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/994289-afr-check-after-new-turbo.html

The over all pressure setting, the idle mixture and the boost adjustment are a back and forth. You move a little in one area and have to adjust the other two.
You will need to lean out (increase pressure) the whole system then adjust the boost setting to not go over 12.5.
I struggled with an over rich on boost for months. I finally increased pressure over the whole range and ended up happy with everything. The only small issue I have now is too lean at first start for about 30 to 90 seconds until the WUR warms up. The AFR's are 15 then come down.
Idle warm 13.5
Cruise in any gear 14 - 14.7 depending on RPM and load
Boost 12 - 12.5
All vary depending on air temp, rpm, ect.

Derrick, makes sense. Thanks for the info. I'll dig in to the link you shared. Based on your numbers, I am indeed rich at idle and cruising, although boost seems good. Are you trying to get that lean issue you mention dialed in or is it acceptable considering the short duration at startup?

Thanks guys for all the feedback. Gives me something to do during this quarantine now that I've got my windshield washer operable again, all my lenses cleaned and leather conditioned.

I’m ok with the brief lean condition at start up.
It was pig rich on boost which is way worse. Boost pushes the extra fuel past the rings and washes the oil off the cylinders. As bad as too lean just takes longer


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